chore(node): preserve pre-canonicalization experiment snapshot

Historical working copy retained for audit before consolidation into main. The canonicalized plugin architecture and later fixes already live in main; this snapshot is not a release or a request to restore obsolete source layout.

apps/node-agent/packaging/preinst

@@ -8,6 +8,12 @@ if [ "$1" = install ] || [ "$1" = upgrade ]; then
       exit 1
     fi
   fi
+  if [ -S /run/mission-core-k1/driver.sock ]; then
+    if ! /usr/bin/python3 -I -c 'import http.client,json,socket; c=http.client.HTTPConnection("k1",timeout=5); c.sock=socket.socket(socket.AF_UNIX); c.sock.settimeout(5); c.sock.connect("/run/mission-core-k1/driver.sock"); c.request("GET","/prepare-safe"); r=c.getresponse(); assert r.status==200 and json.load(r).get("safe") is True'; then
+      echo "Mission Core Node: завершите подключение или запись K1 перед обновлением." >&2
+      exit 1
+    fi
+  fi
   mc_node_device_job=$(systemctl show --property=ActiveState --value mission-core-node-realsense-prepare.service 2>/dev/null || true)
   case "$mc_node_device_job" in
     active|activating) echo "Mission Core Node: дождитесь завершения подготовки устройства." >&2; exit 1 ;;
@@ -20,6 +26,11 @@ if [ "$1" = install ] || [ "$1" = upgrade ]; then
         exit 1
         ;;
     esac
+    # End the admitted idle worker before dpkg replaces its Python modules.
+    # New UI commands now fail unavailable instead of racing the package copy.
+    if [ -f /usr/lib/systemd/system/mission-core-k1.service ]; then
+      systemctl stop mission-core-k1.service
+    fi
   fi
   . /etc/os-release
   if [ "${ID:-}" != ubuntu ] || [ "${VERSION_ID:-}" != 24.04 ]; then